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Author Topic: Missing injector and spark pulses  (Read 17050 times)

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GTRS Fiero

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Missing injector and spark pulses
« on: June 07, 2021, 06:41:49 pm »
When my Fiero gets warm, it starts missing.  When this occurs, it seems that neither the injectors nor the plugs fire.  Once the Fiero cools off (5-10 minutes), it runs OK again.

New plugs, new plug wires, new ICM.   Coils should not affect the injectors.

So, replaced the crank sensor.  Again, because it was leaking oil through the plug.  No change in the misfiring.

Scratched head.  Lost several more hairs.  Problem still not solved.  Wrinkled brow.  Problem still not solved.
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TopNotch

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Re: Missing injector and spark pulses
« Reply #1 on: June 07, 2021, 08:23:14 pm »
What kind of plugs? I tried some "fancy" plugs in my yellow car once. It ran just fine when cold, but lousy when it warmed up.
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GTRS Fiero

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Re: Missing injector and spark pulses
« Reply #2 on: June 07, 2021, 08:39:45 pm »
Stock 3.4 plugs.  But, the missing signal is at the ICM.
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GTRS Fiero

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Re: Missing injector and spark pulses
« Reply #3 on: June 11, 2021, 12:48:31 am »
Not much time, lately, but still struggling with this miss issue.  Everything runs fine--when the engine is cold.  Once it warms up, the car can barely move under its own power.
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Fierofool

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Re: Missing injector and spark pulses
« Reply #4 on: June 11, 2021, 11:40:15 am »
ICM's can break down and cause misfires while still keeping the engine running.  When I bought my 87 in Hickory, NC, it began to misfire on the way home.  Having already owned a Fiero for 7 years, I replaced the ICM and the problem went away.  I suspect the same can happen with a coil pack ICM. 
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GTRS Fiero

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Re: Missing injector and spark pulses
« Reply #5 on: June 11, 2021, 04:58:52 pm »
Not that new ICMs can't be bad, but we replaced it.  No change.
« Last Edit: June 11, 2021, 07:09:14 pm by GTRS Fiero »
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Raydar

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Re: Missing injector and spark pulses
« Reply #6 on: June 11, 2021, 07:04:47 pm »
Quote from: GTRS Fiero on June 07, 2021, 06:41:49 pm
When my Fiero gets warm, it starts missing.  When this occurs, it seems that neither the injectors nor the plugs fire. 
...

If the ECM doesn't see ignition pulses, it turns off the fuel.
(Not sure if it kills the fuel pump or the injectors, but whatever it does, it does.)
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Raydar

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Re: Missing injector and spark pulses
« Reply #7 on: June 11, 2021, 07:07:54 pm »
Quote from: GTRS Fiero on June 11, 2021, 04:58:52 pm
Not that new ICMs csn't be bad, but we replaced it.  No change.

Check the pickup coil. It should read a high resistance. In the thousands of ohms, I think. (Sorry. Not sure. Been a while.)
It'll probably either be good, or "open". Never saw one short out.
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GTRS Fiero

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Re: Missing injector and spark pulses
« Reply #8 on: June 11, 2021, 07:10:43 pm »
Quote from: Raydar on June 11, 2021, 07:04:47 pm
Quote from: GTRS Fiero on June 07, 2021, 06:41:49 pm
When my Fiero gets warm, it starts missing.  When this occurs, it seems that neither the injectors nor the plugs fire. 
...

If the ECM doesn't see ignition pulses, it turns off the fuel.
(Not sure if it kills the fuel pump or the injectors, but whatever it does, it does.)

That function is certainly working.  We replaced the crank position sensor.  No change.  We checked the wiring betweek the CPS and the ICM, good.
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GTRS Fiero

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Re: Missing injector and spark pulses
« Reply #9 on: June 11, 2021, 07:11:17 pm »
Quote from: Raydar on June 11, 2021, 07:07:54 pm
Quote from: GTRS Fiero on June 11, 2021, 04:58:52 pm
Not that new ICMs csn't be bad, but we replaced it.  No change.

Check the pickup coil. It should read a high resistance. In the thousands of ohms, I think. (Sorry. Not sure. Been a while.)
It'll probably either be good, or "open". Never saw one short out.

Not sure that I still have a separate pickup coil.
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Raydar

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Re: Missing injector and spark pulses
« Reply #10 on: June 11, 2021, 07:15:05 pm »
Quote from: GTRS Fiero on June 11, 2021, 07:11:17 pm

Not sure that I still have a separate pickup coil.

Sorry. I forgot that you're running a 7730, now. (Right?)
CPS ought to cover that function, I would think. Not sure, though. Never messed with one.
« Last Edit: June 11, 2021, 07:16:59 pm by Raydar »
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GTRS Fiero

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Re: Missing injector and spark pulses
« Reply #11 on: June 11, 2021, 07:18:32 pm »
Yes.

So, I checked the RPMs, as reported by the ECU.  These are all over the place.  6K at idle, when it's barely able to turn over, zero when it's at idle, and everything in between.

I've been considering that it's a bad ECU.
« Last Edit: June 13, 2021, 11:32:22 pm by GTRS Fiero »
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GTRS Fiero

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Re: Missing injector and spark pulses
« Reply #12 on: June 13, 2021, 11:33:46 pm »
The new CPS died.  Replaced the CPS.  Again.  No change.

Re-worded for clarity.
« Last Edit: June 15, 2021, 01:05:51 am by GTRS Fiero »
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GTRS Fiero

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Re: Missing injector and spark pulses
« Reply #13 on: June 15, 2021, 01:05:02 am »
The engine runs fine, for 10-20 minutes.  Maybe a bit down on power, but smoothly and quietly.  No problem getting up to highway speed.  Then it starts cutting out, and has no power.  Shut it off, and 3 minutes later, it runs normally, again.
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Slyp

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Re: Missing injector and spark pulses
« Reply #14 on: June 15, 2021, 01:25:59 pm »
I had the same sort of problem. I would run fine and then start to miss and stall.  After letting it sit for a while it would be ok........
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